In the petroleum and some other industries, it is sometimes necessary to store large quantities of heavy fluids in a large container and keep an accurate measurement of the amount of fluid within the container. In order to accomplish this task, a sight gage is often used. The level of the fluid is measured by an upper inlet passageway and lower outlet passageway which may be connected to a cylinder which may have a glass wall or window which may be calibrated to indicate the level of the fluid within the container. The glass is susceptible to breakage and leakage especially in an industrial situation. This could lead to a serious leakage of the fluid if left unchecked. It is desired to stop the leak because the fluid may be hazardous, expensive or for cleanliness generally.
A ball check valve has conventionally been employed in the upper and lower passageway of a sight gage which will seat in the passageway when there is breakage or other significant leakage. If the fluid begins to excessively flow towards the sight gage, the ball check valve obstructs the flow of the fluid and thus prevents the leakage of the fluid.
An early example of a ball check valve is disclosed in U.S. Pat. No. 3,113,587 issued on Dec. 10, 1963 to L. A. Hendley. The ball check is normally in a resting position that permits free flow of fluid as shown in FIG. 2 of the patent. If there is excessive flow, the ball check has to be moved to a seated position as shown in FIG. 2A of the patent that should block the flow. The ball should move from the resting position to the blocking position at a situation of excess flow. When the ball is in the blocking position, the inlet pressure maintains the ball check in that position.
Ball check valves are susceptible to leakage, breakage and jamming after repeated use. Ball check valves can also be unreliable in operation, particularly for certain fluids such as petroleum. There may be a buildup on interior surfaces of the valve or a contaminant can become lodged between an interior surface and the ball. In severe cases, the valve may become inoperative due to the ball check not seating properly, allowing fluid to flow past the ball check.